This calculator solves for the fixed monthly instalment on a term loan such as a personal loan, auto loan or fixed-rate business loan, then builds the amortization schedule that shows exactly how much of each payment clears interest versus principal. The output is the number a lender states in the loan agreement before any add-ons like credit insurance or an origination fee taken out of the proceeds.
What counts as a reasonable rate and term
Personal loan pricing tracks credit quality closely: borrowers with strong credit typically see annual rates in the high single digits to low teens, while subprime borrowers routinely see rates from the high teens into the 30s. A quoted rate well outside that band for your credit tier is worth double-checking before you sign.
Auto loan terms have stretched over the past decade, with 72- and even 84-month terms now common on new-vehicle financing. A longer term lowers the instalment but keeps you paying interest on a depreciating asset for years after the car has lost much of its value, so a low payment on a long term is not automatically the cheaper loan.
As a quick sanity check: every 10,000 borrowed at 9% over five years costs roughly 208 a month, and the same amount at 24% over three years costs roughly 392 a month. If your quote is far outside that range for a similar rate and term, re-check the entered numbers before trusting the schedule.
Three loans compared side by side
A 15,000 personal loan at 11.5% over five years (60 months) carries a payment of about 329.89 and total interest of about 4,793 over the life of the loan.
Shorten that same 15,000 loan to three years (36 months) and the rate a strong-credit borrower might actually be offered drops to roughly 8.9%: the payment rises to about 476.30, but total interest falls to about 2,147 — over 2,600 less than the five-year version, even though the rate barely moved.
For a 28,000 auto loan at 6.9%, stretching the term from 60 to 72 months cuts the payment from about 553.11 to about 476.03, a saving of roughly 77 a month, but it adds about 1,087 to total interest over the life of the loan (from roughly 5,187 to roughly 6,274). The extra year buys a lower payment, not a cheaper car.
Why the interest bill is front-loaded
Interest each month is charged on whatever balance is still outstanding, and that balance is largest right at the start, so early payments carry the heaviest interest share even though the total instalment never changes. On the 15,000 loan at 11.5% over five years, roughly 143 of the very first 329.89 payment is interest; by the final year almost the entire payment is principal.
This is also why paying off a term loan early rarely saves as much as borrowers expect once they are more than halfway through the term: most of the interest has already been paid, and what remains to save shrinks fast in the back half of the schedule.
It is the reason a short high-rate loan can beat a longer low-rate one on total cost, and why running the full amortization schedule, not just comparing headline rates, is the only reliable way to compare two competing offers.
Where the amortization math breaks down
The formula assumes one fixed rate applied for the entire term with no missed or late payments. A variable-rate personal loan, a promotional-rate card converted to a term loan, or any loan with a rate that steps up after an introductory period will only match this schedule until the first reset.
It also assumes no prepayment penalty and no fees folded into the loan. An origination fee deducted from the amount disbursed means you receive less than the face value of the loan while still repaying interest on the full amount, which raises the effective rate above the stated one — check the disclosed annual percentage rate rather than the interest rate alone.
Finally, the schedule assumes payments land on time every month. A single missed payment does not just add a late fee; it leaves a larger balance accruing interest into the following month, which compounds the shortfall rather than simply delaying it.
Regional and disclosure differences to check
In the United States, the Truth in Lending Act requires lenders to disclose the annual percentage rate (APR), which folds in most fees, alongside the note rate; comparing offers on APR rather than the headline interest rate is the more reliable comparison.
In the United Kingdom, personal loan advertising must show a representative APR that at least 51% of accepted applicants actually receive, so the rate you are individually offered after a credit check can differ noticeably from the advertised figure.
Some lenders use add-on interest or the rule of 78s to allocate interest across the term instead of standard declining-balance amortization; both produce a different early-payoff balance than the schedule this calculator generates, so ask your lender directly which method applies before relying on this payoff figure to negotiate a settlement.
Frequently asked questions
- How is a monthly loan payment calculated?
- The payment is the fixed amount that fully amortizes the balance over the term at a constant rate: payment equals the loan amount times the monthly rate, divided by one minus (one plus the monthly rate) raised to the power of minus the number of months. On a 15,000 loan at 11.5% over 60 months that works out to about 329.89 a month.
- Why does a longer loan term cost more even at a lower payment?
- Stretching the term lowers the monthly instalment but keeps the balance outstanding, and therefore accruing interest, for longer. On a 28,000 auto loan at 6.9%, moving from 60 to 72 months cuts the payment by about 77 a month but adds roughly 1,087 in total interest.
- How much of my payment goes to interest at the start of the loan?
- Close to half in many cases. On the 15,000 loan at 11.5% over five years, about 143 of the first 329.89 payment is interest and only about 187 reduces the principal; that split flips heavily toward principal by the final year.
- Does paying off a personal loan early always save a lot of interest?
- It saves the most when done early, because the balance and the interest charged on it are largest then. Once you are past the midpoint of the schedule, most of the interest has already accrued and the remaining saving from an early payoff is comparatively small — check your lender's current payoff quote rather than assuming a flat percentage.
- Why is my APR higher than the interest rate I was quoted?
- The APR folds in origination fees and other required charges spread over the loan term, so it is almost always equal to or higher than the bare interest rate. In the US, lenders must disclose APR under the Truth in Lending Act specifically so borrowers can compare loans with different fee structures on one number.
- Should I use a 72-month or 84-month term for a car loan?
- Only if the lower payment is necessary for the budget and you understand you will owe more than the car is worth for longer, which matters if you plan to trade in or the car is written off. On otherwise identical terms, a 60-month loan on the same balance and rate finishes with noticeably less total interest than a 72-month one.
Sources
- Federal Reserve — Consumer Credit (G.19) — Reports average commercial bank interest rates on personal and auto loans by term, updated quarterly through 2025.
- Federal Trade Commission — Truth in Lending Act disclosures — Sets out the requirement that lenders disclose APR, finance charge and payment schedule on closed-end consumer loans.
- UK Financial Conduct Authority — representative APR rules — Explains the requirement that advertised representative APRs be available to at least 51% of accepted applicants (guidance current 2025).